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6Lowpan Working Group                                     S. Daniel Park
Internet-Draft                                       Samsung Electronics
Expires: August 20, 2008                                          K. Kim
                                                         Ajou University
                                                                  E. Seo
                                                             Samsung AIT
                                                          S. Chakrabarti
                                                             IP infusion
                                                             J. Laganier
                                                        DoCoMo Euro-Labs
                                                           February 2008

               IPv6 over Low Power WPAN Security Analysis

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     Copyright (C) The IETF Trust (2008).

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   This document discusses possible threats and security options for
   IPv6-over-IEEE802.15.4 networks.  It is an informational document to
   raise awareness of security issues in IPv6 lowPan networks.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Security Threats . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  6lowpan security analysis  . . . . . . . . . . . . . . . . . . 11
     7.1.  IEEE 802.15.4 Security analysis  . . . . . . . . . . . . . 11
     7.2.  IP Security analysis . . . . . . . . . . . . . . . . . . . 12
   8.  Key Management in 6lowpan  . . . . . . . . . . . . . . . . . . 14
     8.1.  Existing Key management methods  . . . . . . . . . . . . . 14
     8.2.  Issues with Key management in 6lowpan  . . . . . . . . . . 15
   9.  Security consideration in bootstrapping a 6lowpan node . . . . 16
   10. Possible scenarios using different levels of security  . . . . 17
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   14. No I-D References  . . . . . . . . . . . . . . . . . . . . . . 21
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     15.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23

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1.  Introduction

   The principal object of the 6lowpan working group is to design IPv6
   transmission over IEEE 802.15.4 [ieee802.15.4] networks.

   IEEE 802.15.4 [ieee802.15.4] is designed to support variety of
   applications in personal area networks; many of applications are
   security sensitive.

   Specifically, some of the IEEE 802.15.4 optional features actually
   reduce security and implementation would be limited for their
   extensions.  The applications range from defense systems to building
   monitoring, fire-safety, patient monitoring etc.  If the network is
   not secured, an intruder can inject incorrect messages to trigger
   false situations.  Thus link-layer security is quite necessary in
   IEEE802.15.4 networks.

   IEEE 802.15.4 is working on improving the link-layer security
   specification.  However, this document will focus on discussing
   different security threats from the 6lowpan perspective and discuss
   different options of applying existing security methods to overcome
   those threats.  The goal is to provide a trust model using both link-
   layer and IP layer security packages, if possible.

   Designing a new security protocol for 6lowpan network is out of scope
   of this document.  However, it may state desired security
   requirements which can be fed to the appropriate IETF security
   working group in order to suggest appropriate security protocols.

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2.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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3.  Terminology

   This document uses terminology specific to IPv6 and DHCPv6 as defined
   in "Terminology" section of the DHCPv6 specification [RFC3315].

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4.  Overview

   As described in [RFC4919], unlike regular IP network 6lowpan has some
   special characteristics such as small packet size, low bandwidth of
   IEEE 802.15.4 standard [ieee802.15.4], low power, low cost, large
   number of devices, etc.  The security aspect, however, seems a bit
   tradeoff in the 6lowpan since security is always a costly function.
   This is particularly true to low rate WPAN.  Obviously, adding
   security makes the issue even more challenging.  For instance, when
   putting IPv6 on top of 6lowpan, it seems one could use IP security
   and turn off the security of WPAN since the security architecture
   defined by IEEE 802.15.4.  But on the other hand, IP security is
   relatively mature for services at IP or other upper layers.

   It is naturally questionable whether the 6lowpan devices can support
   IP Security (IPSec) as it is.  This document explains some of
   difficulties of adopting IPSec in the following sections.  However,
   Layer 2 security must be used for Layer-2 level operations such as
   MAC sublayer association, beaconing, orphaning, etc.

   Security Considerations paper[802.15.4-ACM] outlines that
   IEEE802.15.4 link-layer provides access control, message integrity,
   message confidentiality and replay-protection services.  Yet the
   document is not clear about key management methods, state of ACL
   table in the event of power loss and support of group keying.
   Network shared common key may be an answer for link-layer security in
   this case, but that is vulnerable with replay attacks and with stolen
   devices.  However, in most common cases, network shared keying may be
   the simple answer to the security at the link-layer for the power-
   deprived, reduced function-devices, as it is easily configurable
   among hundreds of devices.

   IPSec is mandatory to run IPv6, but considering power constraints and
   limited processing capability of the IEEE802.15.4 capable devices
   IPSec may be compute intensive; IKE messaging will not work well in
   low power networks as we want to reduce signaling in this network.
   Thus 6lowpan may need to define its own keying methods that require
   minimum overhead in packet-size and of course a number of signaling
   messages.  IP-layer security will provide authentication and
   confidentiality between end-nodes and across multiple lowpan-links.
   This document later discusses applicability of IP-layer security in
   the case of 6lowpan network usage and applications.  IP-layer
   security may be useful only when two nodes want to send/receive all
   messages securely.  However, in most cases, the security may be
   requested at the application layer as needed, while other messages
   can flow in the network without security overhead.

   The possible threats in this type of network are intrusion, sink-hole

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   and replay attacks.  A third party entity can inject bad routes in
   the network, act as a default router attracting all the packets to
   itself, or it can snoop packets and then launch replay attacks on the
   6lowpan nodes.  These attacks can cause harm especially when the
   attacker is a high-power device, such as a laptop.  It can easily
   drain batteries of the 6lowpan devices by sending broadcast messages,
   redirecting routes etc.

   A possible solution to security issues in the 6lowpan network might
   be application level security (for example, SSL) on top of link-layer
   security.  Link-layer security protects from intrusion in the link
   and the application-level security protects from another user peeking
   at the data and impersonation.

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5.  Security Threats

   Most of the attacks and threats against user and data security in
   6lowpan are plausible and MAY be very destructible in effect, because
   of its wireless radio access and connectivity to the Internet.  The
   security analysis of 6lowpan starts with the appreciation of various
   threats posed at respective ISO OSI layers.  In this section, we
   classify and discuss the threats in layer-wise order.

   6lowpan is highly susceptible to physical attacks. i.e., threats due
   to physical node destruction relocation and masking.  By the Physical
   attacks, 6lowpan nodes can be condemned permanently, so the losses
   are irreversible.  Physical attack can extract cryptographic secrets
   from the associated circuitry, modify programming in the sensors, and
   the malicious node can take control over them.  These compromises can
   result into code modification inside the sensor node to change the
   mission-oriented roles of full fledged networks, let alone sensors.

   In 6lowpan environment, several types of DoS attacks can be triggered
   in different layers.  At the Physical Layer, the DoS attacks could be
   tempering and jamming electromagnetic (EM) signals.  It can be
   executed by swarming the limited resources of 6lowpan devices by the
   high resource devices very easily.  At the Link Layer, it could be
   collision and contention of deliberate stray frames.  At the Network
   Layer, it could be the an outburst of packets in the name of network
   traffic during homing.  At the Transport Layer, attacks could be
   performed by half open and half close TCP segments.  Because of its
   internet connectivity, 6lowpan is highly vulnerable as those kinds of
   attacks can exacerbate.

   Since some 6lowpan nodes might need to work together to execute a
   complete task, there is a burgeoning need to distribute subtasks and
   ensure redundancy of information.  Sybil Attacks MAY also be
   triggered in such 6lowpan environments.  In such a kind of attack, a
   node can pretend to be more than one node, using the identities of
   other sensors.  Sybil attacks MAY be performed against the
   distributed storage, routing mechanism, data aggregation, voting,
   fair resource-allocation and misbehavior detection, etc.  It is not
   very easy to be aware of a Sybil attack in progress, but measuring
   the usage of radio resources, the Sybil attacks MAY be detected,
   though with very little probability.

   In the Black Hole attack, a malicious node acts as a black hole to
   attract all the traffic in the sensor network.  In this attack, the
   attacker listens to requests for routes then replies to the
   requesting nodes that it contains the high quality or shortest path
   to the base station.  Once the malicious device is able to insert
   itself between the communication nodes, it is able to do anything

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   with the packets passing through it.  In fact, this attack can affect
   even the nodes those are spatially farther from the malicious node.

   In the Wormhole attack, the attacker records the packets (or bits) at
   one location in the network and tunnels those to another location.
   Such attacks can be fatal to the working for the 6lowpan, since, this
   sort of attack does not require compromising a sensor in the network;
   rather it could be performed even at the initial phase when the
   sensors start to discover the neighboring information.

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6.  Assumptions

   The [RFC4919] describes two security concerns as follows;

   In Section 4.6 Security: Although IEEE 802.15.4 provides AES link
   layer security, a complete end-to-end security is needed.

   In Section 5 Goals: Security threats at different layers must be
   clearly understood and documented.  Bootstrapping of devices into a
   secure network could also be considered given the location, limited
   display, high density and ad hoc deployment of devices.

   This document will meet the above considerations.

   In addition, existing IP security technologies will be simplified to
   be implemented on the 6lowpan small devices. 6lowpan security
   architecture will shed off lots of fat from IP security technologies
   whenever available.

   IEEE 802.15.4 AES (Advanced Encryption Standard) will be used for
   6lowpan security architecture in conjunction with IP security
   whenever available.

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7.  6lowpan security analysis

   In this section, both IEEE 802.15.4 MAC security and IP security are
   tackled to search for a new 6lowpan trust models and available
   solution spaces if feasible.  The principal object of these analysis
   is to improve 6lowpan security level as we use IP layer security
   mechanism as possible regardless of 802.15.4 vulnerable MAC security.
   802.15.4 MAC enhancement and amendment are not scope of this document
   but IEEE 802 standard stuff.

7.1.  IEEE 802.15.4 Security analysis

   The MAC of IEEE 802.15.4 provides security services that are
   controlled by the MAC PIB (PAN Information Base).  For security
   purpose, the MAC sublayer maintains an access control list (ACL) in
   its MAC PIB.  By specifying a security suite in the ACL for a
   communication peer, a device can indicate what level security should
   be used (i.e., none, access control, data encryption, frame
   integrity, etc.) for communications with that peer.  In addition, MAC
   sublayer offers a secured mode and an unsecured mode.

   A critical function of IEEE 802.15.4 MAC is frame security.  Frame
   security is actually a set of optional services that may be provided
   by the MAC to the upper layers (applications).  The standard strikes
   a balance between the need for these services in many applications,
   and the desire to minimize the burden of their implementation on
   those applications that do not need them.  As described in [802.15.4-
   ACM], if an application does not set any security parameters, then
   security is not enabled by default.  The [ieee802.15.4] defines four
   packet types: beacon packets, data packets, acknowledgements packets
   and control packets for the media access control layer.  It does not
   support security for acknowledgement packets.  But on the other hand,
   other packet types can optionally support integrity protection and
   confidentiality protection for the packet's data field.

   Due to the variety of applications targeted by IEEE 802.15.4, the
   processes of authentication and key exchange are not defined in the
   standard.  Devices without the key cannot decrypt the encryped

   In addition, unsecured mode is suitable for some applications in
   which implementation cost is important, and security is either not
   required or obtained in other ways.  An example of this is that all
   6lowpan devices are assigned a default key by the administrator they
   can exchange data encrypted with that key.  This may work in some
   situations, but this solution is not quite scalable.  In this case,
   802.15.4 node is very vulnerable.

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   The security service enables the MAC to select the devices with which
   it is willing to communicate.  The device may decide to communicate
   with some devices, and not others.  To minimize complexity, the
   access control service is performed on an individual device basis,
   rather than on groups or collections of devices.

   Unlike file transfer or voice communication applications common with
   other protocols, IEEE 802.15.4 applications often transmit messages
   that do not convey secret information.

7.2.  IP Security analysis

   IPsec (IP security protocol) can guarantee integrity and optionnaly
   confidentiality of IP (v4 or v6) packets exchanged between two peers.

   Basically, IPsec works well on non-low-power devices which are not
   subject to severe constraints on host software size, processing and
   transmission capacities.  IPSec supports AH for authenticating the IP
   header and ESP for authenticating and encrypting the payload.  The
   main issues of using IPSec are two-fold: (1) processing power and (2)
   key management.  Since these tiny 6lowpan devices do not process huge
   number of data or communicate with many different nodes, it is not
   well understood if complete implementation of SADB, policy-database
   and dynamic key-management protocol are appropriate for these small
   battery-powered devices.

   Given constraints existing in 6lowpan environments, IPsec might not
   be suitable as is to use in such environments.  Especially, 6lowpan
   node may not be able to operate all IPsec algorithms on its own
   capability either FFD or RFD.

   Bandwidth is a very scarce resource in 6lowpan environments.  The
   fact that IPsec additionally requires another header (AH or ESP) in
   every packet, thus increasing per-packet header overhead, makes its
   use problematic in 6lowpan environments.

   IPsec requires two communicating peers to share a secret key that is
   typically established dynamically with the IKE (Internet Key
   Exchange) protocol.  Thus, it has an additional packet overhead
   incurred by IKE packets exchange.

   If NDP (Neighbor Discovery Protocol) is applied to 6lowpan, SeND
   (Secure Neighbor Discovery) should at least considered to provide
   security in conjunction with neighbor discovery protocol.  So far,
   CGA (Cryptographically Generated Addresses) [RFC3972] and SeND
   options [RFC3971] are newly designed by IETF and it works well over
   existing IP networks.  However, RSA based CGA and SeND options could
   requires larger packet-size and processing time than ECC based keying

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   algorithm.  Therefore, it could be reasonable to use the Secure
   Neighbor Discovery protocol if it is extended to support ECC for
   6lowpan networks application.

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8.  Key Management in 6lowpan

   In order to provide security in 6lowpans, a robust encryption
   mechanism MUST be in place.  Only the non-tamperable keys can provide
   an encryption infrastructure that is thorough enough to provide a
   wide range of security services such as but not limited to
   authentication, authorization, non-repudiation and prevention from
   replay attacks.  In this section, the important issue of key
   management is discussed.

8.1.  Existing Key management methods

   The characteristics of sensors, communicating devices and resulting
   sensor networks, such as limited resources at the node and network
   level, lack of physical protection, unattended operation, and a close
   interaction with the physical environment, all make it infeasible to
   implement some of the most popular key exchange techniques in their
   literal forms for 6lowpans.  In this section, we visit the three
   widely known schemes such as trusted-server scheme, pre-distribution
   scheme and public key cryptography schemes in order to reach to a
   pragmatic key management mechanism for 6lowpans.

   The trusted-server scheme relies solely on the server for key
   agreement between nodes, e.g., Kerberos.  If the server is
   compromised, the trust amongst sensor nodes is severed.  Such a
   scheme is not suitable for sensor networks because there is usually
   no guarantee of communicating seamlessly with a trusted server at all
   the times in sensor networks.

   The key agreement scheme is key pre-distribution, where key
   information is distributed among all sensor nodes prior to
   deployment.  If the network deployers were to know which nodes were
   more likely to stay in the same neighborhood before deployment, keys
   MAY be decided a priori.  However, because of the randomness of the
   deployment, knowing the set of neighbors deterministically might not
   be feasible.  Furthermore, the presence of intruder nodes right from
   the network deployment and initiation time cannot be rejected
   outright as implausible.  Some schemes like network shared keying,
   pair-wise keying, and group keying, have been defined as variants of
   key distribution.  On-site key management mechanisms, while
   warranting the same level of security as key pre-distribution schemes
   have an obvious edge to cope up with network dynamics.

   This class of key management scheme depends on asymmetric
   cryptography, such as public key certificates that are irreversible
   singularly.  This irreversibility comes at a price-often staked by
   the limited computation and energy resources of sensor nodes.
   However, these are the hardest cryptanalyze.  Some of the most

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   popular examples include, but are not limited to Diffie-Hellman key
   agreement, RSA or ECC [RFC2631].  Recent works on ECC implementation
   for low power devices has proven its feasibility for sensor networks.
   It provides security with smaller key size that is comparable to
   security provided by RSA or AES with much higher key size.

   Network topologies for 6LowPan (i.e star and mesh) and presence of
   FFD and RFD makes cluster based dynamic key management schemes the
   most appropriate.  These schemes use Master Keys; Network Keys and
   Links keys which could be pre installed for first round and can be
   distributed by key transport mechanism during later rounds.  This
   scheme provides ease in key distribution and key revocation [ZigBee].

8.2.  Issues with Key management in 6lowpan

   -In a 6lowpan, a malicious node MAY sit amongst other nodes at the
   deployment phase-a problem of secure key assignment at bootstrap

   -A node is compromised during the operating time of 6lowpan-A key
   revocation system MUST be employed.

   -In a sleep-mode enabled 6lowpan, keys to sleeping nodes MUST be
   deprived and reinstated after such nodes resume active state.

   -In case the keys are compromised, a mechanism to diagnose security
   violation MUST be invoked.

   -It SHOULD allow and support dynamic addition of a new node.

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9.  Security consideration in bootstrapping a 6lowpan node

   This section should discuss how does a node configures itself
   securely with a IPv6 router in the network.  It involves assignment
   of IPv6 prefix and the default IPv6 router in the 6lowpan.  Further
   details will be collaborated with 6lowpan commissioning/bootstrapping
   works in near futhre according to the 6lowpan working group

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10.  Possible scenarios using different levels of security

   This section may suggest example scenarios with example solutions in
   different cases (IPSec, SSL, other type of Solutions) although this
   document does not recommend or specify any security solutions.
   Further details will be collaborated with 6lowpan architecture works
   in near futhre according to the 6lowpan working group re-chartering.

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11.  Security Considerations

   This document addresses only security issues around IPv6 over Low
   Power WPAN.

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12.  IANA Considerations

   There is no IANA considerations.

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13.  Acknowledgements

   Thanks to Myungjong Lee at CUNY, USA, Rabia Iqbal, Mustafa Hasan and
   Ali Hammad Akbar all at Ajou University for their valuable comments
   to improve the document.  Special thanks to Jung-Hyun Oh for his
   valuable help on this document.

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14.  No I-D References

   All references shown in this section MUST be added into the
   Informative References before publishing it officially.

   [ieee802.15.4] IEEE Std., 802.15.4-2003, ISBN 0-7381-3677-5, May

   [802.15.4-ACM] Sastry, N. and Wagner, D., Security Considerations for
   IEEE 802.15.4 Networks, ACM WiSE'04, October 2004.

   [ZigBee] Specification Version 1.0, December 2004.

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15.  References

15.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

15.2.  Informative References

   [RFC2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method",
              RFC 2631, June 1999.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, August 2007.

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Authors' Addresses

   Soohong Daniel Park
   System Solution Laboratory, Samsung Electronics.

   Email: soohong.park@samsung.com

   Ki-Hyung Kim
   Ajou University

   Email: kkim86@ajou.ac.kr

   Eunil Seo
   Samsung AIT

   Email: eunil.seo@samsung.com

   Samita Chakrabarti
   IP infusion

   Email: samitac@ipinfusion.com

   Julien Laganier
   DoCoMo Euro-Labs

   Email: lulien.ietf@laposte.net

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Intellectual Property and Copyright Statements

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